Minute to medium sized (1.5-5 mm), yellowish to brown, spider-like, flattened flies without wings. Halteres present. Head small, not adpressed to the thorax but, in resting position, bent backward on to thorax eyes and ocelli small or absent. Legs long with swollen femora and tibiae; first tarsal segment at least as long as all other tarsal segments combined.

The adults are ectoparasites of bats, feeding on their blood. The larvae develop inside the abdomen of the female fly. Just prior to deposition the female leaves her bat host and glues the mature, almost pupated larva (prepupa) to a solid substrate near the resting place of the bats after which the prepupa fairly rapidly forms a puparium. Nycteribiidae show various degrees of host specificity, ranging from species-species associations, through associations with closely related hosts to apparent absence of any host preference.